DE102012206910A1 - Method and device for signaling a transmission time and / or a system clock - Google Patents

Method and device for signaling a transmission time and / or a system clock

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Publication number
DE102012206910A1
DE102012206910A1 DE102012206910A DE102012206910A DE102012206910A1 DE 102012206910 A1 DE102012206910 A1 DE 102012206910A1 DE 102012206910 A DE102012206910 A DE 102012206910A DE 102012206910 A DE102012206910 A DE 102012206910A DE 102012206910 A1 DE102012206910 A1 DE 102012206910A1
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Germany
Prior art keywords
transport data
clock
time information
data packets
transport
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DE102012206910A
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German (de)
Inventor
Norman Herzog
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Rohde and Schwarz GmbH and Co KG
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Rohde and Schwarz GmbH and Co KG
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Priority to DE102011087779.7 priority Critical
Priority to DE102011087779 priority
Application filed by Rohde and Schwarz GmbH and Co KG filed Critical Rohde and Schwarz GmbH and Co KG
Priority to DE102012206910A priority patent/DE102012206910A1/en
Publication of DE102012206910A1 publication Critical patent/DE102012206910A1/en
Application status is Withdrawn legal-status Critical

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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L65/00Network arrangements or protocols for real-time communications
    • H04L65/60Media handling, encoding, streaming or conversion
    • H04L65/601Media manipulation, adaptation or conversion
    • H04L65/602Media manipulation, adaptation or conversion at the source
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04JMULTIPLEX COMMUNICATION
    • H04J3/00Time-division multiplex systems
    • H04J3/02Details
    • H04J3/06Synchronising arrangements
    • H04J3/0635Clock or time synchronisation in a network
    • H04J3/0638Clock or time synchronisation among nodes; Internode synchronisation
    • H04J3/0658Clock or time synchronisation among packet nodes
    • H04J3/0661Clock or time synchronisation among packet nodes using timestamps
    • H04J3/0664Clock or time synchronisation among packet nodes using timestamps unidirectional timestamps
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L65/00Network arrangements or protocols for real-time communications
    • H04L65/60Media handling, encoding, streaming or conversion
    • H04L65/608Streaming protocols, e.g. RTP or RTCP
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/20Servers specifically adapted for the distribution of content, e.g. VOD servers; Operations thereof
    • H04N21/23Processing of content or additional data; Elementary server operations; Server middleware
    • H04N21/236Assembling of a multiplex stream, e.g. transport stream, by combining a video stream with other content or additional data, e.g. inserting a URL [Uniform Resource Locator] into a video stream, multiplexing software data into a video stream; Remultiplexing of multiplex streams; Insertion of stuffing bits into the multiplex stream, e.g. to obtain a constant bit-rate; Assembling of a packetised elementary stream
    • H04N21/23608Remultiplexing multiplex streams, e.g. involving modifying time stamps or remapping the packet identifiers
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/20Servers specifically adapted for the distribution of content, e.g. VOD servers; Operations thereof
    • H04N21/23Processing of content or additional data; Elementary server operations; Server middleware
    • H04N21/242Synchronization processes, e.g. processing of PCR [Program Clock References]
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/60Network structure or processes for video distribution between server and client or between remote clients; Control signalling between clients, server and network components; Transmission of management data between server and client, e.g. sending from server to client commands for recording incoming content stream; Communication details between server and client 
    • H04N21/63Control signaling related to video distribution between client, server and network components; Network processes for video distribution between server and clients or between remote clients, e.g. transmitting basic layer and enhancement layers over different transmission paths, setting up a peer-to-peer communication via Internet between remote STB's; Communication protocols; Addressing
    • H04N21/643Communication protocols
    • H04N21/6437Real-time Transport Protocol [RTP]
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00Details of television systems
    • H04N5/04Synchronising
    • H04N5/06Generation of synchronising signals
    • H04N5/067Arrangements or circuits at the transmitter end
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04JMULTIPLEX COMMUNICATION
    • H04J3/00Time-division multiplex systems
    • H04J3/02Details
    • H04J3/06Synchronising arrangements
    • H04J3/0635Clock or time synchronisation in a network
    • H04J3/0638Clock or time synchronisation among nodes; Internode synchronisation
    • H04J3/0658Clock or time synchronisation among packet nodes
    • H04J3/0661Clock or time synchronisation among packet nodes using timestamps
    • H04J3/067Details of the timestamp structure

Abstract

A method of signaling a time and / or a clock by a headend (7) generating a transport data stream of video and / or audio data to at least one receiver (19, 241, 242, ...) of the transport data stream iteratively calculates the in time information (PCRN + 1; RTPN + 1; TN + 1) from the time information (PCRN; RTPN; T1) of the last transport data packet sent in the transport data stream with integrated time information, a transmission time since the last transmitted transport data packet with integrated time information data bits transmitted in the transport data stream and a clock (fPCR; fSys). The time information (PCRN + 1, PCRN, RTPN + 1, RTPN, TN-1, T1) is used in each case for signaling times or a clock and each contains a number of pulses of the clock (fPCR, fSys) counted up to the transmission time of the respective transport data packet.

Description

  • The invention relates to a method and a device for signaling a transmission time and / or a system clock, in particular in a digital television transmission system.
  • In a digital television broadcasting system, such as the American Advanced Television Systems Committee (ATSC) standard or the European Digital Video Broadcast (DVB) standard, a head-end station belonging to the broadcaster and transmit to the individual television receivers time information for the reconstruction or synchronization of the system clock used in the broadcaster and for determining the display time based on this system clock of each individual image of the television transmission on the screen of the television receiver.
  • In the Moving Picture Expert Group (MPEG) coding used in television transmission - Motion Picture Engine Group Coding - the system clock used in the broadcasting station in the Program Clock Reference (PCR) field becomes the program reference clock Field - an MPEG encoded transport data packet the display time of an image on the screen of the television receiver in the presentation time stamp (PTS) field (presentation time stamp field) of an MPEG encoded transport data packet and the time of decoding an image in TV receiver in the decoding time stamp (DTS) field (decoding time stamp field) of an MPEG-encoded transport data packet transmitted from the headend of the broadcaster to the television receiver.
  • In addition, the transmission times of the individual MPEG-encoded transport data packets of the transport data stream transmitted by the headend to the individual television receivers are transmitted between the headend of the broadcaster and one of the headend downstream output adapter or between the headend of the broadcaster and the individual stations of a common wave network.
  • While the system clock and the instants for displaying an image or outputting a sound, or for decoding an image or a sound, are already being generated by the video or audio source in the studio, respectively the recorded video and audio data Pack in transport data packets or control data belonging to the recorded program transport data stream or elementary data stream, the individual transmission times of the individual transport data packets are determined only in the generation of a transport data stream in the studio downstream headend.
  • The system clock is obtained in the video or audio source on the basis of accumulated clock pulses of a source belonging to the video or audio source clock source and transmitted as time information in certain transport data packets of a transport data stream or in certain control data of an elementary data stream to the head-end. In the head station, the time information containing the system clock is packed in transport data packets of the transport data stream. In addition, in the head station, the transmission times of the individual transport data packets are obtained on the basis of accumulated clock pulses of a clock source belonging to the head station and also stored as time information in certain transport data packets of the transport data stream.
  • The accuracy of the system clock stored in this way in the time information fields of the individual transport data streams or elementary data streams and of the individual stored transmission times is very much dependent on the accuracy of the clock sources used in each case. Unfortunately, while the clock source of a video or audio source typically has a good clock accuracy on average, the clock source used in a head-end process computer is characterized only by a low clock accuracy in the short-term horizon. The timing accuracy of the long term horizon clock source used in the headend is due to time synchronization of the clock source used in the headend with a good clock timing reference clock source, such as the Global Positioning System (GPS) or Network Time Protocol (NTP) reference clock ) Server, in a larger time frame comparatively well.
  • From the DE 10 2009 057 362 A1 A method for generating a transport data stream in a television transmission system is known, in which the clock source used in the studio has a significantly poorer clock accuracy than the clock source used in the head station. The clock accuracy of the clock source belonging to the clock source, which typically only has a high clock accuracy in the long-term horizon, this is improved by interpolation of the responsible for the long-term horizon clock of an NTP server in its clock accuracy in the short-term horizon. Despite interpolation, the clock source of the headend station has an unwanted phase jitter that affects the timing accuracy of the headend Clock source even in the short-term horizon in an insufficient for the requirements of today's television transmission systems quality leaves.
  • The object of the invention is therefore to provide a method and a device for generating and transmitting time information - in particular the system clock used and the exact transmission times of the individual transport data packets of the transport data stream - which are characterized by a high clock or timing accuracy.
  • The object is achieved by an inventive method for signaling a time and / or a clock with the features of claim 1 and by an inventive device for signaling a time and / or a clock with the features of claim 24. Advantageous technical extensions of the invention are listed in the respective dependent claims. Claim 38 or 39 relates to a corresponding computer program or computer program product.
  • According to the invention, the time-in particular the transmission time of the individual transport data packet-and the clock-in particular the system clock-are not determined on the basis of the comparatively inaccurate clock of the clock source integrated in the head station, but computed in the head station and transmitted as time information in a transport data packet to the respective receiver. in the case of the transmission time of a transport data packet to the output adapter or to the individual transmitting stations or in the case of the system clock to the television receiver - transferred. The time information stored in a transport data packet results from the number of pulses of a clock accumulated up to the transmission time. The calculation is carried out iteratively by the time information stored in a transport data packet from the time information transferred in a last transmitted transport data packet plus the pulse number of the clock accumulated between the transmission time of the two transport data packets, which in turn results from the multiplication of the transmission time between the two transport data packets by the clock , is calculated.
  • The transmission time between the two transport data packets again results from the quotient of the number of data bits transmitted in the transmission time between the two transport data packets and the data rate of the transport data stream.
  • In a first preferred embodiment of the invention, the number of transmitted data bits between the transmission times of two successive transport data packets, each with integrated time information, the data rate in the case of signaling a system clock thus for calculating the time information stored in each transport data packets as pure arithmetic the transport data stream and the time information of the last integrated with integrated time information transport data packet used. As an additional quantity used in the calculation, the clock of the real clock reconstructed in the head-end station of the clock source contained in a video or audio source is used.
  • In a second preferred embodiment of the invention, in the event of a transmission time of a transport data packet for calculating the time information stored in the individual transport data packets, particular arithmetic variables, namely the number of transmitted data bits between the transmission times of two successive transport data packets each having integrated time information, the data rate of the transport data stream, the time information of the last integrated with integrated time information transport data packet and the nominal value of the system clock used.
  • Thus, with the signaling according to the invention of a calculated system clock and / or a calculated transmission time, the clock inaccuracy of the clock source integrated in the head station of the prior art is eliminated and a correct system clock and comparatively correct transmission times are transmitted to the respective receivers.
  • In the case of the signaling of a system clock, the real clock of the clock source present in a video or audio source is preferably transmitted from the video or audio source via transport data packets of a transport data stream with integrated time information to the head station. For this purpose, the pulse number of the real clock of the clock source accumulated at the time of transmission of a data packet with integrated time information is stored as time information in the currently transmitted data packet.
  • When using an MPEG-encoded transport data stream for the transmission of digital precompressed video data via an asynchronous serial interface (ASI) interface - asynchronous serial interface - the accumulated at the time of transmission of the respective transport data packet pulse number are preferably stored in the PCR field of the transport data packet , When using a non-encoded elementary data stream for the transmission of digital uncompressed video data via a serial data interface (SDI) interface - serial data interface - the accumulated number of pulses at the time of transmission of data of an image in control data, in particular in a synchronizing bit pattern, which at the beginning of the data contained in the information of an image is inserted into the elementary data stream. Finally, for the transmission of digital pulse code modulation (PCM) -modulated - pulse code modulated - audio data in an elementary data stream via an audio engineering socity-3 (AES3) audio engineering company - the accumulated number of pulses at the time of transmission An audio data associated with an image is transferred into control data, in particular a synchronizing bit pattern, which is inserted into the elementary data stream at the beginning of the data containing the audio information.
  • In the head-end station, the real clock of the clock source used in a video or audio source is preferably reconstructed by determining the difference between the time information of two consecutive transport data packets or control data, each with integrated time information, through the input adapters upstream of one of the headend stations Receive times of the associated transport data packets or control data are divided with each integrated time information. The reception time of a transport data packet or of control data in the input adapter results from the accumulated number of pulses of a clock source integrated in the input adapter at the time of receipt of the transport data packet or the control data whose frequency accuracy is higher than the frequency accuracy of the in the video or audio source existing clock source is.
  • Since the clock rate reconstructed in the head station of the clock source used in the video or audio source due to the average good timing accuracy of this clock source over the nominal system clock to a falsification of each stored in the individual transport data packets time information for signaling the system clock, this is reconstructed clock in the head station preferably limited in terms of its frequency deviation and frequency drift to a predetermined by the transmission standard maximum frequency deviation value and maximum frequency drift value.
  • In the case of signaling a transmission time for a transport data packet, several transport data packets are combined to form a network of transport data packets, which has its own header - data packet header - in which the time information determined for the combination of transport data packets is stored, for reasons of efficiency. In this way, only a single time information for a number of integrated transport data packets must be transmitted instead of time information for each individual transport data packets. Preferably, a real-time transport protocol (RTP) data packet - real-time transport protocol data packet - which consists of a certain number of transport data packets is used as a combination of transport data packets. In the case of using a network of transport data packets instead of individual transport data packets, the iterative calculation of the time information stored in each case in a combination of transport data packets preferably uses the transmitted data bits between in each case two successive transmitted networks, each with integrated time information.
  • The transport data packets sent by the head-end station are transmitted via a local packet-oriented network, preferably via a packet-oriented network operating according to the Internet Protocol (IP) Internet Protocol, to an output adapter downstream of the head-end station. In the output adapter, the individual transport data packets or networks of transport data packets, preferably RTP transport data packets, are buffered in an intermediate memory until the transmission time of the respective transport data packet. In this way, different transmission delays of the individual transport data packets or of the individual networks of transport data packets in the local packet-oriented network due to a different intensity of transmission in the network are collected.
  • The transport data packets sent by the head-end station are alternatively transmitted via a local packet-oriented network, preferably via a packet-oriented network operating according to the Internet protocol, directly to the individual transmitting stations installed in a single-frequency network. Equivalently, the received transport data packets or networks of transport data packets, preferably RTP transport data packets, are buffer-stored in a buffer memory until the transmission time of the respective transport data packet.
  • The time interval between the transmission times of two successive transport data packets to be transmitted in the case of the transmission of networks of transport packets between the head station and the output adapter or the individual transmitting stations is preferably in the output adapter or in individual transmitting stations from the integer quotient between the difference in two successive Following transmitted networks of transport data packets respectively calculated time information and the number of transport data packets contained in a composite calculated. In order to further increase the accuracy of the determined time interval between the transmission times of two transport data packets to be transmitted consecutively in the case of the transmission of networks of transport data packets, a correction value stored in a table is added to the determined time interval, which is to be sent from the position of the respective Transport data packet in the combination of transport data packets and depends on the fractional part of the quotient.
  • A transport data packet is preferably transmitted in the output adapter or in the transmitting station as soon as the accumulated number of pulses of a clock of a clock source integrated in the output adapter or in the transmitting station has reached the corrected number of clock pulses since the transmission time of the last transmitted transport data packet which is in the time interval between the transmitter times two consecutive to be sent transport data packets fall.
  • The clock source in the output adapter or in a transmitting station has a comparatively high clock accuracy with respect to the system clock in the short-term horizon, while its clock accuracy with respect to the system clock in the long-term horizon is comparatively insufficient. To increase the clock accuracy of the clock source in the output adapter or in a transmitting station in the long-term horizon, the frequency of a voltage-controlled frequency oscillator integrated in the clock source is preferably regulated in a control loop. As a control variable in this control loop normalized with the nominal system clock time difference between the longest cached in the buffer transport data packet and the caching least cached transport data packet is used, which normalized with the nominal system clock time difference between the longest cached in the buffer memory transport data packet and the in the buffer acting as a buffer memory the shortest cached transport data packet in an initialization time with respect to a setpoint deviation compared with.
  • Thus, there is no pure level control, in which the number of transport data packets in the buffer memory is controlled to a constant value, but a control of the nominal system clock normalized difference of transmission times between the longest and the shortest in the buffer cached transport data packets to a constant value. If, due to a longer-term frequency drift of the clock source integrated in the output adapter or in a transmitting station, an accelerated or delayed transmission of the individual transport data packets in the long-term horizon, this results in a smaller or higher number of transport data packets buffered in the buffer memory and a reduction or Increasing the difference between transmission times between the longest and the shortest stored in the buffer memory transport packets noticeable. This reduction in the setpoint deviation reduces or increases the frequency of the frequency oscillator integrated in the clock source. In this way it is ensured that the difference between transmission times between the longest and the shortest stored in the buffer memory transport packet is controlled to the prevailing at initialization constant difference value and thus the periodicity between the individual transmission times in the long-term horizon retains a constant value.
  • The buffer level and thus the normalized with the nominal system clock difference of transmission times between the longest and the shortest stored in the buffer transport data packets is not due to the transmission jitter in the network between the headend and output adapter or transmitting station and the sudden increase in the buffer level on receipt of a composite of transport data packets constant. In order to obtain a usable measured value for the normalized with the nominal system clock difference of transmission times between the longest and the shortest stored in the buffer transport data packets, this value is preferably determined in each case at the individual receiving times of a network of transport data packets and the maximum value from all over followed by a certain time interval values as the most trustworthy value.
  • In the transmission of networks of transport data packets, the buffer memory preferably consists of a first sub-buffer for storing the received networks of transport data packets and a second sub-buffer coupled to the first sub-buffer in which the from the composite unpacked transport data packets that are sent in the next transmission times are stored.
  • For smoothing step-shaped setpoint deviations at the transitions of the individual time intervals, a pre-filter and for smoothing high-frequency components in the setpoint deviation is preferably present in the control loop in front of the controller. For example, in the case of superimposed noise, an averaging filter is provided in front of the controller. The controller preferably has a proportional control behavior in order not to worsen the dynamics of the control loop unnecessarily and at the same time to realize a control difference of zero for existing integrating behavior of the controlled system - level range.
  • The existing clock inaccuracy of the clock of the clock source used in the output adapter or in a transmitting station relative to the nominal system clock is preferably limited in the control loop by a regulator connected downstream of the level limiter to a predetermined by the respective transmission standard maximum frequency deviation. An existing frequency drift of the clock of the clock source used in the output adapter or in a transmitting station relative to the nominal system clock is additionally limited in the control loop by a flank limiter connected downstream of the controller to a maximum frequency drift predetermined by the respective transmission standard.
  • Embodiments of the method according to the invention and of the device according to the invention for signaling a transmission time and / or a system clock in a digital television transmission system will be explained below in detail with reference to the drawing. The figures of the drawing show:
  • 1 a block diagram of an embodiment of the transmitter side of a digital television transmission system,
  • 2 a block diagram of an embodiment of the video or audio source,
  • 3 a block diagram of an embodiment of the input adapter,
  • 4 a block diagram of an embodiment of the head-end station,
  • 5 a block diagram of an embodiment of the output adapter according to the invention and a transmitting station according to the invention,
  • 6 a table with correction values depending on the position of the transport data package in the compound and the fractional component,
  • 7 a table with the number of received RTP packets, RTP packet spacing and RTP packet number in the buffer as a function of the data rate,
  • 8th a time diagram of the buffer level in the buffer memory,
  • 9A . 9B . 9C a data structure of an embodiment of an RTP data packet header, an RTP data packet header extension and an RTP data packet header extension with time information for individual transport data packets and
  • 10 a flowchart of a method according to the invention for signaling a transmission time and / or a system clock in a digital television transmission system.
  • In the following, the inventive method for signaling a transmission time and / or a system clock in a digital television transmission system using the flowchart in 10 in combination with those in the 1 to 5 illustrated components of the inventive device for signaling a transmission time and / or a system clock in a digital television transmission system explained.
  • In the first method step S10 of the method according to the invention are according to 1 in the individual video or audio sources 1 1 , 1 2 , .., 1 i ,., 1 n generates a transport data stream with transport data packets or an elementary data stream with digital data, each containing video data or audio data. The single video or audio source 1 i according to 2 contains a video or audio Data Generator 2 i , for example a TV camera for generating digital video data or an audio recording system for generating digital audio data. A video or audio data generator 2 i generates a precompressed digital transport data stream with ASI protocol standard digital, typically MPEG encoded video transport data packets, an uncompressed digital elementary data stream with digital non-encoded video data according to the SDI protocol standard, or a digital elementary data stream with digital PCM data. modulated audio data according to the AES3 protocol standard.
  • The individual transport data packets or data streams with video or audio data are stored in a subsequent output buffer 3 i cached. The individual transport data packets or data streams become one of the video or audio sources at the rate f Si 1 i associated clock source 4 i from the output buffer 3 i read out and in this clock f si to one of the headend 7 upstream input adapter 6 i transfer. The clock f Si of the respective clock source 4 depends on the protocol standard used and can also vary within a protocol standard used. The timing accuracy of the clock f S1 , f S2 , ..., f Si , ..., f Sn in a video or audio source 1 1 , 1 2 , .., 1 i ,., 1 n used clock source 4 1 , 4 2 , ..., 4 i , ..., 4 n compared to the system clock of an MPEG-encoded television transmission in the amount of 27 MHz, for example, typically 30ppm and is therefore in a good average accuracy range.
  • The representation of the individual video belonging to each image in the television receiver at the right time, in relation to the recording time of the respective image in the video or audio source 1 i stands, the television receiver in the case of transmission of image data in MPEG-coded data packets according to the ASI standard, the recording time of the respective image on the accumulated up to the recording time number of clock pulses in the video or audio source 1 1 , 1 2 , .., 1 i ,., 1 n used clock source 4 1 , 4 2 , ..., 4 i , ..., 4 n in the PTS field in the data packet header (header) of the transport data packet transmitting the image data of the respective image by the video or audio source 1 i signals.
  • In the case of transferring image data in uncoded digital data streams in accordance with the SDI standard, the recording timing of the respective image is determined by the number of clock pulses accumulated in the video or audio source up to the recording time 1 1 , 1 2 , .., 1 i ,., 1 n used clock source 4 1 , 4 2 , ..., 4 i , ..., 4 n via associated control data, preferably via associated synchronization bit patterns, in the digital data stream before the data containing the first line of the respective image by the video or audio source 1 i signals.
  • In the case of transmission of audio data in uncoded digital data streams according to the AES3 standard, the recording timing of the sound associated with the respective image becomes higher than the number of clock pulses accumulated in the video or audio source up to the recording time 1 1 , 1 2 , .., 1 i ,., 1 n used clock source 4 1 , 4 2 , ..., 4 i , ..., 4 n via associated control data, preferably via associated synchronization bit pattern, in the digital data stream before the audio data through the video or audio source 1 i signals.
  • Equivalent to the television receiver is the timing and thus the order of decoding the individual transport data packet, in turn, in relation to the time and thus the order of encoding of the respective transport data packet in the video or audio source 1 i stands for time information in the DTS field of the respective transport data packet through the video or audio source 1 i signals.
  • Since the time information stored in the PTS and DTS field of the respective transport data packet as pulse number of the clock in the respective video or audio source 1 i integrated clock source 4 i be won, the television receiver is the clock of the respective clock source 4 i about time information, which in turn is the number of pulses of the clock of the clock source 4 i are signaled in the PCR fields of each successive transport data packets. In the case of non-coded video data, the time information required for the reconstruction of the clock in the television receiver is stored in an appropriate field immediately before the first video data of an image in the elementary data stream. Equivalently, in the transmission of PCM-modulated audio data, the time information required to reconstruct the clock in the television receiver is placed in an appropriate field directly in front of the audio data in the elementary data stream.
  • To signal the clock in a video or audio source 1 i integrated clock source 4 i to a television receiver in the next step S20, the pulses of the clock of the clock source 4 i one unit 5 i for determining the number of pulses supplied at the time of transmission of the transport data packet or the control data and counted there. From the information in the output buffer 3 i cached transport data packet or which in the output buffer 3 i cached control data at which clock pulse of the clock source 4 i is or will be sent by the unit 5 i for determining the number of pulses at the time of transmission, the number of pulses of the clock of the clock source counted at the time of transmission of the respective transport data packet to be transmitted or of the respective control data to be transmitted 4 i stored as time information in the respective transport data packet or in the respective control data.
  • The individual transport data streams or elementary data streams are from the individual video or audio sources 1 1 , 1 2 , ..., 1 i , ..., 1 n to respectively assigned input adapters 6 1 , 6 2 , ..., 6 i , ..., 6 n transmit, each one a headend 7 are upstream. In a respective input adapter 6 i according to 3 The individual transport data packets of the respective transport data stream or the data of the respective elementary data stream are in an associated input buffer 8th i cached before going into a subsequent conversion unit 9 i from the respective transmission protocol used - ASI, SDI, AES3, etc. - in a uniform transmission protocol of a packet-oriented network, preferably in an Internet Protocol (IP) - Internet Protocol -, and then in an associated output buffer 10 i be outsourced.
  • In the respective input adapter 6 i become in the following process step S30 in a unit 11 i for determining the reception time of a data packet, the reception times of those transport data packets or control data determined, each containing a time information. For this purpose, in turn, the number of pulses of the clock accumulated at the time of reception of the respective transport data packet or of the control data is one for the respective input adapter 6 1 , 6 2 , ..., 6 i , ..., 6 n belonging clock source 12 1 , 12 2 , ..., 12 i , ..., 12 n determined. The timing accuracy of the clock f T1 , f T2 , ..., f Ti , ..., f Tn of such a clock source 12 1 , 12 2 , ..., 12 i , ..., 12 n compared to the system clock of an MPEG-coded television transmission is relatively high at about +/- 1ppm. The determined reception times of the individual transport data packets or control data with integrated time information are from the unit 11 i for determining the reception time of a data packet in unused fields of the associated IP-based data packets for transmission to the headend 7 deposited.
  • The data packets of the individual transport data streams according to the ASI standard or the individual data of the elementary data streams according to the SDI or AES3 standard are converted into individual data packets of a data packet stream for transfer via a packet-oriented local network 13 packed and out of the output buffers 10 1 , 10 2 , .., 10 i , .., 10 n the single input adapter 6 1 , 6 2 , ..., 6 i , ..., 6 n via the packet-oriented local network 13 , in particular via the Internet, to the headend 7 according to 4 transferred and there in the associated input buffers 13 1 , 13 2 , ..., 13 i , ..., 13 n filed.
  • In the subsequent method step S40, the clock sources become 4 1 , 4 2 , ..., 4 i , ..., 4 n of the individual video or audio sources 1 1 , 1 2 , ..., 1 i , ..., 1 n respective real clocks f PCR in one to the head station 7 belonging entity 14 for the reconstruction of the clock of a clock source based on in each successive data packets N and N + 1 of the individual data packet streams integrated time information PCR N + 1 and PCR N and the transmitted reception times
    Figure 00210001
    reconstructed according to equation (1).
    Figure 00210002
  • The in the individual entrance buffers 13 1 , 13 2 , ..., 13 i , ..., 13 n cached data packets of the individual data packet streams are in the next step S50 in subsequent encoders 15 1 , 15 2 , ..., 15 i , ..., 15 n respectively encoded to MPEG-compliant transport data packets and in associated buffers 16 1 , 16 2 , ..., 16 i , ..., 16 n cached after encoding. The individual transport data packets of the individual elementary transport data streams are in the same method step S50 in a multiplexer 17 merged into a common transport stream.
  • In one to the head station 7 belonging calculation unit 18 are used to signal the timing of each video or audio source 1 1 , 1 2 , ..., 1 i , ..., 1 n integrated clock sources 4 1 , 4 2 , ..., 4 i , ..., 4 n to the television receiver from that in the previous unit 14 for the reconstruction of the clock of a clock source determined clock f PCR a clock source for a reconstruction of the clock in Television receiver required time information in each successive transport data packets with integrated time information iteratively determined according to equation (2).
    Figure 00220001
  • For this purpose, according to equation (2), the time information PCR N + 1 in a transport data packet N + 1 iteratively from the time information PCR N of the last transmitted transport data packet N by adding the multiplied by the reconstructed clock f PCR quotient between the number of data bits N bits (T N + 1 ) - N bits (T N ), which are transmitted between the respective consecutive transmitted transport data packets N + 1 and N, and the data rate f TS of the transport data stream.
  • In one to the calculation unit 18 subsequent unit 41 For limiting the frequency of the time information, the time information necessary for the signaling of the clock to the individual video or audio source 1 1 , 1 2 , ..., 1 i , .., 1 n respective clock sources 4 1 , 4 2 , ..., 4 i , ..., 4 n are adapted in each successive transport data packets N and N + 1 with respect to a limitation of the frequency deviation and the frequency drift of the reconstructed clocks f PCR . In this way, it is ensured that a frequency deviation or a frequency drift of the clocks of these clock sources 4 1 , 4 2 , ..., 4 i , ..., 4 n remains within certain limits as a result of a measurement error in the detection of the reception times of the individual transport data packets or control data with integrated time information and thus the individual time information (PCR, PTS, DTS) are correctly reconstructed in the television receiver within a limited accuracy.
  • In the same calculation unit 18 are used to signal the transmitter times of the individual transport data packets to one of the head stations 7 downstream output adapter 19 or to the individual transmitting stations 24 1 , 24 2 , ... of a single-frequency network which determines the transmitter times respectively transmitting time information of two consecutive transport data packets with integrated time information iteratively.
  • In order not to transmit an associated transmission time for each individual transport data packet, which would markedly worsen the efficiency of the transmission, a time information including a transmission time is determined and transmitted only for a specific number of transport data packets. From this transmitted time information, the transmission time of each individual transport data packet is reconstructed in the output adapter or in the transmitting stations of the single-frequency network.
  • In a first variant, in each case one transmission time is transmitted for each Nth transport data packet, from which time the transmission times of the remaining N - 1 transport data packets are determined. The time information T N + 1 in the N + 1 th transport data packet containing the transmission time of the N + 1 th transport data packet can be calculated from equation (3A) from the time information T 1 in the first transport data packet containing the transmission time of the first transport data packet by adding the with the nominal System clock f Sys of an MPEG coded television transmission (27 MHz) multiplied by the ratio of the number of transmitted data bits N bits (T N + 1 ) - N bits (T 1 ) between the first and the N + 1 th transport data packet and the Determine data rate f TS of the transport data stream.
    Figure 00240001
  • In a second variant, which will be considered in more detail below, n transport data packets are combined to form a network of transport data packets, and the transmission time of the network of transport data packets is stored in header data packet header of the network of transport data packets. Preferably, as a combination of transport data packets, the so-called real-time transport protocol (RTP) - real-time transport protocol - used on the application layer - application layer - summarizes several transport data packets to a composite of transport data packets and with a corresponding RTP data packet header provides.
  • For the iterative calculation of a time information RTP N + 1 stored in an RTP transport data packet N + 1 , according to equation (3B), the quotient of the number N bits (T N +.) Multiplied by the nominal system clock f Sys of an MPEG-coded television transmission is multiplied 1 ) - N bits (T N ) of the data bits transmitted between the RTP transport data packet N and the RTP transport data packet N + 1 and the data rate f TS of the Transport data stream to the time information RTP N of a last constructed and transmitted RTP transport data packet N added.
    Figure 00250001
  • The second variant of the invention is preferable to the first variant of the invention, since the transmission of the time information relevant to the system clock in the header of the individual transport data packets is separated from the transmission of the time information relevant to the transmission times in the header of a RTP transport data packet preferably selected as a composite of transport data packets and thus the assignment of the individual time information is uniquely determined and no additional transmission information reducing the efficiency of the transmission is to be transmitted.
  • The individual time information is from the calculation unit 18 - In the case of a system clock-containing time information after the interposition of the unit 41 for limiting the frequency of time information - the multiplexer 17 is made available and inserted in the same method step S70 in the corresponding fields of the header of the individual transport data packets or RTP transport data packets. The thus generated for the transmission of individual transport data packets of the common transport data stream are in a multiplexer 17 downstream output buffer 19 cached until dispatch.
  • The individual transport data packets of the common transport data stream are transmitted at a specific data rate. The timing of the common transport data stream via the clock f R one of the headend 7 assigned clock source 20 , This clock source has a comparatively poor clock accuracy over the nominal system clock of digital television transmission in the short-term horizon (typically +/- 100 ppm). In a long-term synchronization unit 21 this is in the short-term horizon comparatively inaccurate clock of the clock source 20 with the long-term stable clock of a reference time server 25 For example, a Network Time Protocol (NTP) server - Network Time Protocol Server - synchronized in the long-term horizon. The individual data bits of the individual transport data packets of the common transport data stream are combined with the output clock of the long-term synchronization unit 21 via a local packet-oriented data network 22 , preferably over the Internet, to the output adapter 19 or via a packet-oriented wide area network 23 , which is also preferably an IP-based network, to the individual transmitting stations 24 1 , 24 2 , ... a common wave network sent (so-called transport stream over IP-based network (Transport Stream over Internet Protocol (TSoverIP))).
  • The in the output adapter 19 or in the individual transmitting stations 24 1 , 24 2 , ... received transport data packets are in the next step S80 each in a buffer 26 stored. In the first sub-variant of the invention, this buffer is 26 a single cache while the cache 26 in the second variant of the invention from a first sub-buffer 26 1 , in which the individual received and not yet unpacked networks of transport data packets, ie preferably the individual not yet unpacked RTP transport data packets, are stored, and a second sub-buffer 26 2 , in which unpacked transport data packets are stored.
  • A transmission of an RTP transport data packet from the first sub-cache 26 1 to the second sub-cache 26 2 is done on request by the second sub-buffer 26 2 , once in the second sub-cache 26 2 no more individual transport data packets are included.
  • In the same processing step S80, the transmission times of the individual transport data packets become one unit 27 determined for determining the transmission time of a transport data packet.
  • In the case of the first variant of the invention, the unit reads 27 for determining the transmission time of a transport data packet, the time information T 1 and T N + 1 of two spaced at intervals of N transport data packets transport data packets with integrated time information and determined according to equation (4A) in the time difference between the two time information T 1 and T N + 1 falling number of pulses ΔT. ΔT = T N + 1 - T 1 (4A)
  • In the case of the second variant, the unit reads 27 to determine the transmission time of a transport data packet in two successive transmitted networks of transport data packets N and N + 1 respectively transmitted time information RTP N and RTP N + 1 and determined according to equation (4B) in the time difference between the two time information RTP N and RTP N + 1 falling pulse number ΔRTP. ΔRTP = RTP N + 1 - RTP N (4B)
  • After a division of the pulse number ΔT according to equation (4A) or the pulse number ΔRTP according to equation (4B) by the number of pulses_TS_ packets and a subsequent determination of the integer component int (.) Results in accordance with equation (5) in the transmission time Distance between two consecutively to be sent transport data packets falling pulse number Δ TS packet . Δ TS-Packet = int (ΔRTP / Number_TS_ Packets) or = int (ΔT / Number_TS_ Packets) (5)
  • The determination of the integer portion is required on the one hand to send out the individual transport data packet to a specific integer number of clocks, but on the other hand leads to an inaccuracy of the transmission time of the individual transport data packets relative to the respective exact transmission time at the nominal system clock of MPEG-encoded television transmission. When integrating time information only into every seventh transport data packet or when integrating seven transport data packets into one RTP data packet, it is possible for the transmission time of a single transport data packet to result in an erroneous delay of up to six system clocks, i. a delay of no longer tolerable 222 ns at a system clock of 27 MHz.
  • In order to minimize this intolerable delay, depending on the position of a transport data packet between two transport data packets each with integrated time information in the case of the first variant of the invention or the position of a transport data packet in the combination of transport data packets in the case of the second variant of the invention and in dependence fractional portion of the division between the number of pulses ΔRTP or ΔT and the number of number_TS_ packets in a composite of transport data packets according to the in 6 shown table for each transport data packet a correction value added to the respectively determined transmission time. In this case, a transmission of time information in each seventh transport data packet or a transmission of seven transport data packets in a network is assumed. In this way, the delay in the transmission time of a transport data packet is minimized to a maximum of a single system clock.
  • The calculation of the number of pulses ΔRTP between the time information RTP N and RTP N + 1 transmitted in two consecutive RTP data packets N and N + 1 and a pulse number and the number of pulses falling in the transmission time interval between two transport data packets to be transmitted consecutively Δ TS packet and the correction by the respective correction value in the second variant of the invention immediately after the transfer of an RTP data packet from the first sub-buffer 26 1 to the second sub-cache 26 2 in the unit 27 for determining the transmission time of a transport data packet.
  • The determination of an optimized transmission time for each transport data packet according to the above described procedure requires a constancy of the data rate of the transport data stream during the transmission time between two transport data packets with integrated time information or during the transmission time of the network of transport data packets. If the data rate of the transport data packet is not constant, then in a third variant of the invention for each transport data packet that is transmitted in an RTP data packet, time information for signaling the respective transmission time point in an RTP data packet header extension can be transmitted.
  • An RTP data packet header according to 9A for this purpose has an optional field "RTP data packet header extension", which indicates an extension of the RDP data packet header by additional fields. These additional fields of the RTP data packet header extension according to 9B are defined in length in the "length" field and have an extension of 4 bytes proportional to the length of the "length" field. In 9C If there are seven transport data packets in an RTP data packet, the associated seven transmission times are shown in the respective fields of the RTP data packet header extension.
  • In this way, the transmission times of the individual transport data packets transmitted in an RTP data packet no longer have to be transmitted on the basis of a single data packet transmitted in an RTP data packet Time information to be calculated, but are in advance in the calculation unit 18 the headend 7 calculated and stored in the individual fields of the RTP data packet header extension. Alternatively, in a fourth variant of the invention, the transmission time of a transport data packet can also be transmitted as time information in each individual transport data packet. Thus, in the third and fourth variants of the invention, the data rate of the transport data stream can vary over time within the transmission time of an RTP data packet, without falsifying the transmission time of the individual transport data packets.
  • The transmitted or determined transmission times of the individual transport data packets each represent pulse counts of the nominal system clock. The real transmission time of the individual transport data packet results when the transmitted or determined transmission times of the individual transport data packets with the accumulated number of pulses of the clock f of the A output adapter 19 or the broadcasting stations 24 1 , 24 2 , ... of the common wave network respectively associated clock source 28 correspond. The clock f A of the clock source 28 Although has a relatively high clock accuracy over the nominal system clock in the short-term horizon (typically +/- 1 ppm), the long-term stability of the clock f A clock source 28 but is not very high in comparison. Thus it comes in the intermediate buffer 26 after a certain time, an undesirable overflow or idle.
  • To avoid overflow or idling of the intermediate buffer 26 in the next method step S90, the clock source 28 as a voltage-controlled and typically temperature-compensated frequency oscillator 29 realized whose frequency as a function of the setpoint deviation serving as a control variable time interval between the longest and the shortest in the intermediate buffer 26 cached transport data packets is controlled and thus the long-term stability of the clock of the clock source 28 is realized.
  • In this context, in an intermediate buffer 26 downstream unit 30 for determining the maximum transmission time interval of the transport data packets in the buffer memory starting from the above-described determination of an optimized transmission time for each transport data packet, the transmission time of the longest in the intermediate buffer 26 located transport data packet - this is in the case of the second variant of the invention, a in the second partial buffer memory 26 2 unpacked from the respective network of transport data packets transport data packet - and the transmission time of the shortest in the buffer 26 located transport data packet - this is in the case of the second variant of the invention, a in the first partial buffer memory 26 1 in the last received composite of transport data packets contained and not yet unpacked transport data packet that is placed in the last position in the composite - determined.
  • Since the transmission time of the individual transport data packet results from the multiplication of the time information transmitted in the transport data packet and the nominal system clock, this is independent of the data rate f TS of the transport data stream. A temporal change of the data rate f TS of the transport data stream thus has, with the application of the transmission time interval between the longest and the shortest in the intermediate buffer 26 cached transport data packet as a controlled variable in contrast to the application of the number of in the buffer 26 cached data bits and / or transport data packets as a control variable no effect on the control result and must for the frequency control of the voltage-controlled frequency oscillator 29 also not known. This is in 5 shown.
  • The buffer level of the buffer 26 - determined as the number of in the intermediate buffer 26 located transport data packets - has in the case of the second variant of the invention on a time-varying course. He is according to 8th by an unsteady increase in the individual reception times of a network with a plurality of transport data packets in the intermediate buffer 26 and characterized by a much steadier drop due to the sending of the individual transport data packets to each different transmission times and thus by maxima. Since the transmission time of the individual networks of transport data packets in the local packet-oriented network 22 between head station 7 and output adapter 19 or in the packet-oriented long-range network 23 between head station 7 and broadcasting station 24 1 , 24 2 , ... fluctuates due to the time-dependent network load, the individual maxima are in the buffer level of the buffer 26 , like out 8th shows, different levels. Since the associations of transport data packets with the lowest transmission time to a buffer level of the cache 26 lead, which is most meaningful, is in the case of the two variant of the invention in one of the unit 30 for determining the maximum transmitter time interval of the transport data packets in the buffer memory subsequent maximum value investigator 31 determined over a suitable period of time, the maximum value of the time interval between the shortest and the longest cached in the buffer memory data packet, which represents the most reliable control variable determined.
  • For the selection of a suitable period for maximum value determination, the in 7 shown in the table in which a transmission of seven transport data packets in an RTP data packet and a buffer depth of 100 msec. for the cache 26 for each different data rates for an MPEG-encoded transport data stream, the number of in the intermediate buffer 26 RTP data packets received per second, the time interval between two received RTP data packets and the number of times in the buffer 26 RTP data packets are shown. In order to achieve a sufficient number of received RTP data packets and thus a sufficient number of maxima in the period for maximum value determination given parameters, a period for the maximum value determination of preferably 100 msec. recommended.
  • This ascertained maximum value is used in a subsequent sample-and-hold element which is likewise used only in the two variants of the invention 32 held over the period of maximum value determination and in a subsequent subtractor 33 subtracted from a setpoint to determine a setpoint deviation. As a setpoint, the maximum time interval between the longest and the shortest stored in the intermediate buffer transport data packet is determined at the initialization time and then used.
  • In one, to the subtractor 33 subsequent pre-filter 34 sudden changes in the setpoint deviation, in particular discontinuities in the setpoint deviation at the individual transitions of the maximum value determination periods, are smoothed. A the pre-filter 34 subsequent averaging filter 35 performs with its low-pass characteristic smoothing of high-frequency components in the setpoint deviation, in particular a smoothing of superimposed noise components in the setpoint deviation, by. The averaging filter 35 iteratively determines an averaged setpoint deviation y i + 1 at the sampling time i + 1 from the averaged setpoint deviation y i at the sampling time i and the unmediated setpoint deviation y i at the sampling time i via a sliding exponential averaging with the weighting factor α according to equation (6). The weighting factor α is preferably designed in powers of two, so that the averaging filter 35 computationally only by shift operations and fixed point arithmetic. y i + 1 = (1-α) · y i + α · y i (6)
  • The pre-filtered and averaged setpoint deviation becomes a controller 36 supplied, which has a purely proportional controller behavior with a suitably dimensioned gain K P. This way the controller adds 36 no additional delay in the control loop and ensures at the same time in an integrating controlled system and a suitably dimensioned gain factor K P a setpoint deviation, which is negligible after the settling time of the control loop.
  • The proportional controller 36 closes a level limiter 37 indicating a frequency deviation of the voltage-controlled frequency oscillator 29 limited to a standard according to the transmission standards maximum frequency deviation. For an MPEG-encoded ATSC transport stream with an SMPTE310M interface, an absolute frequency deviation of less than +/- 2.8 ppm is provided for the parameterization of the level limiter 37 is set and thus a medium-term fluctuation, ie a wandering, the frequency of the voltage-controlled frequency oscillator 29 in derogation. In addition, in one of the level limiter 37 adjoining flank limiters 38 a limitation of the frequency drift of the voltage-controlled frequency oscillator 29 to a maximum frequency drift dictated by transmission standards. For an MPEG encoded transport stream with an ASI interface, the frequency drift is limited to 75 mHz per second. At this maximum value of a frequency drift is the edge limiter 38 parameterized.
  • Via a serial digital interface 39 this is limited in terms of frequency deviation and frequency drift and by the regulator 36 generated digital control signal in series to the input of a digital-to-analog converter 39 transmit and thus a different clock rate between the edge limiter 38 and the digital-to-analog converter 39 overcome. In the digital-to-analog converter 39 becomes the digital output signal of the edge limiter 38 corresponding analog value for controlling the voltage-controlled frequency oscillator 29 determined. The resolution of the digital-to-analog converter 39 is to be chosen such that a minimum change of the digital control signal at the output of the edge limiter 38 at the level of the lowest-value data bit at a significantly lower than the maximum possible frequency drift change in the frequency of the voltage-controlled frequency oscillator 29 leads.
  • In the regulated state of the control loop corresponds to the Transmission time interval between the in the buffer 26 the longest and shortest stored transport data packet the set value, ie the transmission time interval between the in the buffer 26 the longest and shortest stored transport data packet at the time of initialization.
  • In the final step S100, the individual are in the buffer 26 cached transport data packets sent at their respective transmission times.
  • In the case of the third and fourth variant of the invention, in each case one transmission time point in the head station for each transport data packet 7 is determined and transmitted, the respective real transmission time is present when in the unit 27 to determine the transmission time of a transport data packet contained in the time information of the respective transport data packet to be transmitted pulse number of the system clock with the counted pulse count of the clock f A to the output adapter 19 or to the transmitting station 24 1 , 24 2 , ... belonging clock source 28 matches.
  • In the case of the first or second variant of the invention, in each case only the transmission time of a transport data packet in a sequence of transport data packets as time information from the headend 7 to the output adapter 19 or to the transmitting station 24 1 , 24 2 , ..., while the transmission times of the remaining transport data packets in the sequence of transport data packets in the output adapter 19 or in the transmitting station 24 1 , 24 2 , ... is calculated at the output of the transport data packet whose transmission time already in the head-end station and only by a correction value in the unit 27 is corrected to determine the transmission time of a transport data packet, the same procedure for real transmission time as in the third or fourth variant of the invention.
  • In the transport data packets of the first and second variant of the invention, for each in the unit 27 to determine the transmission time of a transport data packet, the transmission time distance Δ TS packet is calculated for each previously to be sent transport data packet and corrected by a correction value is corrected by the respective correction value airtime interval Δ TS packet as the number of pulses of the system clock with the since Transmission time of the last transmitted transport data packet counted pulse number of the clock f A to the output adapter 19 or to the transmitting station 24 1 , 24 2 , ... belonging clock source 28 compared and activated the identity of the output of the respective transport data packet.
  • The in the output adapter 19 output transport data packets are via an ASI interface using a working according to the synchronous digital hierarchy (SDH) -multiplexing dedicated line to the individual transmitting stations 24 1 , 24 2 , ... of the common wave network.
  • The input adapters 6 1 , 6 2 , ..., 6 i , ..., 6 n as well as the output adapter 19 can also be in the headend 7 be integrated, with the traffic between the input adapters 6 1 , 6 2 , ..., 6 i , ..., 6 n and the process computer of the headend 7 and between the process computer of the head-end station 7 and the output adapter 19 via an internal bus system instead of a local network 13 and 22 be realized. Such a technical embodiment is also covered by the invention.
  • The invention is not limited to the illustrated individual embodiments and variants. Of the invention, in particular all combinations of all claimed in the individual claims features, all disclosed in the description features and all features shown in the figures of the drawing with covered.
  • QUOTES INCLUDE IN THE DESCRIPTION
  • This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.
  • Cited patent literature
    • DE 102009057362 A1 [0008]

Claims (39)

  1. Method for signaling a time and / or a clock by a head-end station generating a transport data stream from video and / or audio data ( 7 ) to at least one recipient ( 19 . 24 1 , 24 2, ...) of the transport data stream by iteratively calculating the integrated in a transport data packet of the transport stream time information (PCR N + 1; RTP N + 1; T N + 1) (from the time information PCR N; RTP N; T 1) of the last transport data packet transmitted in the transport data stream with integrated time information, a transmission time of data bits transmitted with integrated time information in the transport data stream since the last transmitted transport data packet and a clock (f PCR , f Sys ), the time information (PCR N + 1 , PCR N ; RTP N + 1 , RTP N ; T N + 1 , T 1 ) in each case serve to signalise times and / or a clock and in each case contain a number of pulses of the clock (f PCR , f Sys ) counted up to the transmission time of the respective transport data packet.
  2. Method according to Claim 1, characterized in that the transmission time of data bits transmitted since the last transmitted transport data packet with integrated time information in the transport data stream is the quotient of the number (N bits (T N + 1 ) -N bits (T N )) since the last transmitted transport data packet with integrated time information in the transport data stream transmitted data bits and the data rate (f TS ) of the transport data stream corresponds.
  3. Method according to claim 1 or 2, characterized in that the signaled clock in the head-end station ( 7 ) reconstructed clock (f PCR ) of a clock source ( 4 1 , 4 2 , ..., 4 i , ..., 4 n ) a video and / or audio source ( 1 1 , 1 2 , ..., 1 i , ..., 1 n ) which generates a transport data stream from transport data packets or an elementary data stream from serially transmitted data.
  4. Method according to claim 3, characterized in that a time information belonging to an image or to a sound is stored in a data packet header or in control data of one of the video and / or audio source ( 1 1 , 1 2 , ..., 1 i , ..., 1 n ) generated transport data packet or elementary data stream a counted number of pulses of the clock to the video and / or audio source ( 1 1 , 1 2 , ..., 1 i , ..., 1 n ) associated clock source ( 4 1 , 4 2 , ..., 4 i , ..., 4 n ) at the recording time of the picture or sound.
  5. A method according to claim 3 or 4, characterized in that the clock (f S1 , f S2 , ..., f Si , ..., f Sn ) of the video and / or audio source ( 1 1 , 1 2 , ..., 1 i , ..., 1 n ) associated clock source ( 4 1 , 4 2 , ..., 4 i , ..., 4 n ) from the integrated time information (PCR N + 1 , PCR N ) and the determined time of reception
    Figure 00420001
    is reconstructed from two consecutive transmitted in the received elementary stream data packets.
  6. Method according to one of claims 3 to 5, characterized in that the reception times
    Figure 00420002
    of two consecutive transport data packets or control data with integrated time information with the clock (f T1 , f T2 , ..., f Ti , ..., f Tn ) of a clock source ( 12 1 , 12 2 , ..., 12 i , ..., 12 n ) one of the head stations ( 7 ) upstream input adapter ( 6 1 , 6 2 , ..., 6 i , ..., 6 n ) whose frequency stability is higher than the frequency stability of the clock (f S1 , f S2 ,..., f Si ,..., f Sn ) compared to a nominal system clock (f Sys ) for video and / or audio -Source ( 1 1 , 1 2 , ..., 1 i , ..., 1 n ) associated clock source ( 4 1 , 4 2 , ..., 4 i , ..., 4 n ) is opposite to the nominal system clock (f sys ).
  7. Method according to one of claims 1 to 6, characterized in that in the head station ( 7 ) reconstructed clock (f PCR ) of the video and / or audio source ( 1 1 , 1 2 , ..., 1 i , ..., 1 n ) is limited in terms of its frequency deviation and / or frequency drift.
  8. Method according to one of claims 1 to 7, characterized in that the transport data packet with integrated time information of the transport data stream is an MPEG-encoded transport data packet with an integrated PCR time information.
  9. Method according to one of claims 3 to 6, characterized in that the elementary data stream received in an SDI interface unencoded data stream with digital uncompressed video Data having a time information characterizing the beginning of an image and / or a coded data stream received in an AES3 interface with PCM-coded digital audio data having time information indicative of the beginning of audio data of the elementary data stream associated with an image.
  10. Method according to one of claims 1 to 9, characterized in that the signaled time of the sending time of a transport data packet of the transport data stream in one of the headend ( 7 ) downstream output adapter ( 19 ) or in a transmitting station ( 24 1 , 24 2 , ...) whose clock source ( 28 ) each have a higher time accuracy in a short time horizon than the clock source ( 20 ) of the head station ( 7 ) having.
  11. Method according to Claim 10, characterized in that for the purpose of iteratively calculating a time information (RTP N + 1 ; T N + 1 ) associated with a transport data packet in dependence on a time information (RTP N ; T 1 ) associated with a transport data packet preceding each transport data stream, a nominal System clock (f sys ) is used.
  12. The method of claim 10 or 11, characterized in that a plurality of transport data packets of the transport data stream are combined into a network and for the composite of several transport data packets time information (RTP N + 1 , RTP N ) is transmitted in the data packet header of the network.
  13. Method according to Claim 12, characterized in that, for the iterative calculation of the time information (RTP N + 1 ) integrated in a network of several transport data packets and signaling a transmission time of the network, the number (N bits (T N + 1 ) - N bits (T N )) is used between data bits to be transmitted between two successive networks.
  14. A method according to claim 12 or 13, characterized in that in the output adapter ( 19 ) or in the transmitting station ( 24 1 , 24 2 , ...) received transport data packets are buffered until the respective transmission time, wherein in the transmission time interval between two consecutively transmitted transport data packets falling pulse number (.DELTA. TS packet ) from the integer quotient of the difference (.DELTA.RTP) in two integrated time information (RTP N + 1 , RTP N ) is calculated by the number (number_TS_ packets) of the transport data packets contained in a network.
  15. Method according to Claim 14, characterized in that a correction value dependent on the fractional component of the quotient and the order of the respective transport data packet within the network is added to the number of pulses (Δ TS packet ) falling in the transmission time interval between two consecutively transmitted transport data packets .
  16. A method according to claim 14 or 15, characterized in that a transport data packet in the output adapter ( 19 ) or in a transmitting station ( 24 1 , 24 2 , ...) is sent as soon as the clock source ( 28 ) of the output adapter ( 19 ) or the transmitting station ( 24 1 , 24 2 , ...) since the transmission time of the last transmitted transport data packet generated number of clock pulses of the falling in the transmission time interval of two consecutively transmitted transport data packets falling number of pulses (.DELTA. TS packet ) corresponds.
  17. Method according to one of claims 12 to 16, characterized in that the composite of several transport data packets is an RTP data packet in which a certain number of transport data packets is included.
  18. Method according to Claim 17, characterized in that the time information of the transport data packets respectively contained in the RTP data packet is transmitted in an extended data packet header of the RTP data packet.
  19. Method according to one of claims 10 to 16, characterized in that the accuracy of the clock to the output adapter ( 19 ) or to a transmitting station ( 24 1 , 24 2 , ...) associated clock source ( 28 ) is stabilized with respect to the long term by the frequency of one in the clock source ( 28 ) integrated frequency oscillator ( 29 ) is regulated as a function of a setpoint deviation of the normalized with the nominal system clock (f Sys ) difference between the time information of the longest cached transport data packet and the shortest cached transport data packet.
  20. Method according to one of claims 10 to 16 or 19, characterized in that the time information of the longest and the shortest in the output adapter ( 19 ) or in a transmitting station ( 24 1 , 24 2 , ...) cached transport data packets in the reception time of each network of several transport data packets in the output adapter ( 19 ) or in a transmitting station ( 24 1 , 24 2 , ...) are detected.
  21. Method according to one of claims 10 to 16, 19 or 20, characterized in that a maximum value of all differences determined within a certain time interval between the time information of the longest and the shortest in the output adapter ( 19 ) or in a transmitting station ( 24 1 , 24 2 , ...) is determined between buffered transport data packets and compared with a difference that is determined at an initialization time and serves as a setpoint for determining the setpoint deviation.
  22. A method according to claim 19, characterized in that the setpoint deviation before a control in a proportional controller ( 36 ) is supplied to a pre-filtering for smoothing step-shaped setpoint deviations and an averaging filter for smoothing higher-frequency components in the setpoint deviation.
  23. A method according to claim 22, characterized in that the controller ( 36 ) generated control signal a level limiter ( 37 ) for limiting the frequency deviation of the clock (f A ) in the output adapter ( 19 ) or in a transmitting station ( 24 1 , 24 2 , ...) used clock source ( 28 ) from the nominal system clock (f Sys ) to a maximum frequency deviation and / or an edge delimiter specified by a transmission standard transmission standard ( 38 ) for limiting the frequency drift of the clock (f A ) in the output adapter ( 19 ) or in a transmitting station ( 24 1 , 24 2 , ...) used clock source ( 28 ) is supplied to a predetermined by a transmission standard for transport streams maximum frequency drift.
  24. Device for signaling a time and / or a clock by a head station generating a transport data stream from video and / or audio data ( 7 ) to at least one recipient ( 19 ; 24 1 , 24 2 , ...) of the transport data stream with one encoder ( 15 1 , 15 2 , .., 15 i , .., 15 n ) for generating transport data packets from individual transport data packets or data respectively transmitted in a transport data stream or an elementary data stream, to a multiplexer ( 16 ) for generating a transport data stream from the individual transport data packets and a calculation unit ( 18 for the iterative calculation of a time information integrated in a transport data packet of the transport data stream (PCR N + 1 , RTP N + T , T N + 1 ) Dependence of a time information (PCR N , RTP N , T 1 ) integrated in a transport data packet preceding in the transport data stream the time information (PCR N + 1 , PCR N , RTP N + 1 , RTP N , T N + 1 , T 1 ) each signal times or a clock.
  25. Apparatus according to claim 24, characterized in that for signaling a clock of the calculation unit ( 18 ) one unity ( 14 ) is connected upstream for the reconstruction of a clock of a clock source.
  26. Apparatus according to claim 25, characterized in that for the reconstruction of the clock (f S1 , f S2 , ..., f Si , ..., f Sn ) one in a video and / or audio source ( 1 1 , 1 2 , ..., 1 i , ..., 1 n ) integrated clock source ( 4 1 , 4 2 , ..., 4 i , ..., 4 n ) the head station ( 7 ) an input adapter ( 6 1 , 6 2 , ..., 6 i , ..., 6 n ) with an integrated clock source ( 12 1 , 12 2 , ..., 12 i , ..., 12 n ) and a unit ( 11 i ) are preceded to determine the reception time of a transport data packet or control data.
  27. Device according to claim 25 or 26, characterized in that for the determination of the time information of a clock source integrated in a transport data packet or in control data ( 4 1 , 4 2 , ..., 4 i , ..., 4 n ) a video and / or audio source ( 1 1 , 1 2 , ..., 1 i , ..., 1 n ) one unit each ( 5 i ) is followed by determining the pulse number of the transmission time.
  28. Device according to one of claims 25 to 27, characterized in that in the head station ( 7 ) one unity ( 41 ) is provided for limiting the frequency of the time information.
  29. Device according to one of Claims 24 to 28, characterized in that in one of the head stations ( 7 ) downstream output adapter ( 19 ) or in one of the head stations ( 7 ) downstream transmitting station ( 24 1 , 24 2 , ...) in each case a buffer ( 26 ) is present for the intermediate storage of the transport data packets of the received transport data stream.
  30. Apparatus according to claim 29, characterized in that for the time-synchronous transmission of the transport data packets in the respective transmission time in the output adapter ( 19 ) and / or in the transmitting station ( 24 1 , 24 2 , ...) one unit each ( 27 ) for determining the transmission time of a transport data packet and a clock source ( 28 ) are provided.
  31. Apparatus according to claim 30, characterized in that for long-term stabilization of the frequency and the frequency drift of the clock source ( 28 ) of the output adapter ( 19 ) or the transmitting station ( 24 1 , 24 2 , ...) a control circuit for controlling the frequency of one in the clock source ( 28 ) integrated frequency oscillator ( 29 ) as a function of a setpoint deviation of a difference between the time information in the buffer ( 26 ) is provided on the longest and shortest cached transport data packets.
  32. Device according to one of claims 29 to 31, characterized in that the temporary storage ( 26 ) one unity ( 30 ) for determining the maximum transmission time interval of the transport data packets in the buffer memory ( 26 ) is connected downstream.
  33. Device according to one of claims 29 to 32, characterized in that for determining a maximum difference between the time information of the in the buffer ( 26 ) the longest and shortest stored transport data packets over a particular time interval ( 30 ) for determining the maximum transmission time interval of the transport data packets to the buffer memory ( 26 ) a maximum value investigator ( 31 ) is connected downstream.
  34. Apparatus according to claim 31, characterized in that for regulating the setpoint deviation, a controller ( 36 ) is provided with a proportional control behavior.
  35. Device according to claim 34, characterized in that the regulator ( 36 ) for smoothing step-shaped setpoint deviations a prefilter ( 34 ) and / or for smoothing higher-frequency components in the setpoint deviation an averaging filter ( 35 ) are connected upstream.
  36. Device according to claim 34 or 35, characterized in that the regulator ( 36 ) a level limiter ( 37 ) for limiting the frequency deviation of the clock in the output adapter ( 19 ) or in a transmitting station ( 24 1 , 24 2 , ...) used clock source from the nominal system clock to a predetermined by a transmission standard for transport streams maximum frequency deviation and / or an edge limiter ( 38 ) to limit the frequency drift of the clock in the output adapter ( 19 ) or in a transmitting station ( 24 1 , 24 2 , ...) used clock source ( 28 ) are connected downstream to a predetermined by a transmission standard for transport streams maximum frequency drift.
  37. Device according to one of claims 29 to 36, characterized in that in the case of integration of multiple transport data packets in a network of transport data packets in the output adapter ( 19 ) or in the transmitting station ( 24 1 , 24 2 , ...) integrated buffers ( 26 ) from a first sub-buffer ( 26 1 ) for temporarily storing the received networks of transport data packets and one with the first partial buffer memory ( 26 1 ) coupled second partial buffer memory ( 26 2 ) for intermediate storage of individual transport data packets.
  38. Computer program with program code means for carrying out all steps according to one of the claims 1 to 23, when the program is executed on a computer or a digital signal processor.
  39. A computer program product having program code means, in particular stored on a machine-readable medium, for carrying out all the steps according to one of claims 1 to 23 when the program is executed on a computer or a digital signal processor.
DE102012206910A 2011-12-06 2012-04-26 Method and device for signaling a transmission time and / or a system clock Withdrawn DE102012206910A1 (en)

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US14/363,464 US9729598B2 (en) 2011-12-06 2012-12-06 Method and a device for signalling transmission time and/or a system clock
CN201280060450.9A CN103975600B (en) 2011-12-06 2012-12-06 The method and apparatus of transmission time and/or system clock pulse is sent with signal
PCT/EP2012/074587 WO2013083668A1 (en) 2011-12-06 2012-12-06 Method and device for signaling a transmission time and/or a system clock pulse

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US20140362873A1 (en) 2014-12-11

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